1. Field of the Invention
The present invention relates to a vertical type nitride semiconductor light emitting diode, and, more particularly, to a vertical type nitride semiconductor light emitting diode, which has a bonding pad of an n-side electrode formed adjacent to an edge of an upper surface of an n-type nitride semiconductor layer serving as a light emitting surface for the nitride semiconductor light emitting diode, thereby preventing a wire bonding portion from shielding light emitted from the light emitting surface, and which has an extended electrode of the n-side electrode formed in various shapes from the bonding pad, thereby preventing concentration of current density.
2. Description of the Related Art
Generally, a nitride semiconductor refers to a III-V group semiconductor crystal, such as GaN, InN, AlN and the like, and is generally utilized for a light emitting device, which can emit light in a short wavelength range (from ultraviolet light to green light), especially blue light.
Since the nitride semiconductor light emitting diode is manufactured by use of an insulating substrate, such as a sapphire substrate, which satisfies lattice matching requirements for crystal growth, it has a horizontal structure in which two electrodes respectively connected to p-type and n-type nitride semiconductor layers are substantially aligned horizontal to an upper surface of the light emitting structure.
Due to the horizontal structure as described above, the nitride semiconductor light emitting diode has several disadvantages. First, a path for electric current is narrowly formed in the horizontal direction from an n-side electrode to a p-side electrode through an active layer. Due to such a narrow path of electric current, the nitride semiconductor light emitting diode having the horizontal structure exhibits increased forward voltage Vf, and thus is lowered in current efficiency.
Furthermore, since the nitride semiconductor light emitting diode of the horizontal structure is increased in heat generation amount caused by an increase in current density, and since low heat conductivity of a sapphire substrate thereof results in insufficient heat dissipation, thermal load is increased between the sapphire substrate and the nitride semiconductor light emitting structure, causing mechanical stress to be applied therebetween, so that the diode becomes unstable.
Furthermore, since areas of an active layer and a p-type nitride semiconductor layer removed for forming the n-side electrode must be larger than an area of the n-side electrode formed by a subsequent process, the nitride semiconductor light emitting diode of the horizontal structure has a reduced light emitting area, thereby reducing light emitting efficiency depending on brightness with respect to a size of the diode.
In order to enhance the disadvantages of the nitride semiconductor light emitting diode having the horizontal structure, a vertical type nitride semiconductor light emitting diode from which the sapphire substrate is removed by a laser lift-off process has been actively developed.
FIGS. 1a and 1b are a side view and a top view illustrating a conventional vertical type nitride semiconductor light emitting diode. Referring to FIGS. 1a and 1b, when manufacturing the conventional nitride semiconductor light emitting diode, an n-type nitride layer 11, an active layer 12, and a p-type nitride layer 13 are sequentially formed on a sapphire substrate, and then the sapphire substrate is removed by the laser lift-off process. In this construction, the n-type nitride layer 11 becomes the uppermost layer, and an upper surface thereof is used as a light emitting surface. Accordingly, the conventional nitride semiconductor light emitting diode comprises the n-type nitride layer 11, the active layer 12, the p-type nitride layer 13, a conductive bonding layer 14, and a conductive supporting substrate 15 sequentially formed in this order from the top of the nitride semiconductor light emitting diode. The nitride semiconductor light emitting diode 13 further comprises an n-side electrode 16 formed on an upper surface of the n-type nitride semiconductor layer 13, such that a wire bonding portion is provided to the n-side electrode 16 for supplying electric current.
As shown in FIGS. 1a and 1b, the conventional vertical type nitride semiconductor light emitting diode has the n-side electrode 16 formed at the center of the upper surface of the n-type nitride semiconductor layer 11 which is the light emitting surface. When the n-side electrode 16 is formed at the center of the upper surface of the n-type nitride semiconductor layer 11, there occurs a problem in that a wire W connected to the n-side electrode 16 by wire bonding shields light emitted from the upper surface of the n-type nitride semiconductor layer.
Meanwhile, when the n-side electrode 16 is formed near an edge of the n-type nitride semiconductor layer 11, current density is concentrated on the bottom of the n-side electrode 16 due to excellent conductivity of the n-type nitride semiconductor layer 11, thereby reducing an effective area for emitting the light.
Accordingly, in order to solve the problem of shielding light by the wire bonding portion, there is a need to provide a nitride semiconductor light emitting diode with a vertical structure, which has a new electrode structure, designed to have the n-side electrode formed adjacent to an edge of the n-type nitride semiconductor layer while ensuring effective distribution of current density.